Yellowstone spokesman Dan Hottle said the Steamboat geyser, which is notoriously unpredictable and had been known to go decades without erupting, shot out a stream of water Wednesday, CNN reported Friday.
"We estimate this eruption was about 200 to 300 feet high, and then it just steamed for about 24 hours," Hottle said.
He said 30 or 40 people witnessed the eruption of the geyser, located in the Norris Geyser Basin in Wyoming.
"For us, it's exciting. Every time you're down there, you wonder if that'll be the time that it erupts," he said.